Low Density Poly Ethylene (LDPE) is produced in an autoclave and/or tubular reactor at high pressure and temperature. High pressure, free-radical polymerizations are disclosed in the following references: U.S. Pat. Nos. 8,445,606, 4,135,044, 7,582,709, and JP050534422 (Abstract). The tubular process is preferred over the autoclave process by its capability to increase ethylene conversion. It would be desirable to combine the higher ethylene conversion potential of a tubular process with maximum flexibility in product design as function of Molecular Weight Distribution (MWD) and rheological properties, such as melt-index and melt strength (MS). MWD and MS are influenced by the process conditions, such as reactor type, pressure and temperature conditions and monomer ethylene conversion, while the product melt-index is controlled with the level of chain transfer agent (CTA). Typically, broad MWD resins are made using higher max. polymerization temps. in each reaction zone, while narrow MWD resins are made by using lower max. polymerization temps. in each zone, and thus, broad MWD resins are consequently made at higher monomer ethylene conversion and polymer output, while the narrow MWD resins are made at lower ethylene conversion and lower polymer output. Another important parameter is the polymer output of a high pressure polymerization process, which can range from 40 to 450 KTA or higher.
The polymer output of a tubular process is affected by ethylene conversion and monomer throughput. The ethylene conversion is governed by the desired product properties. The monomer throughput depends on the design and the operating conditions of a hyper compressor system, which compresses the monomer feed stream to the required reactor inlet pressure. Another parameter of importance is the energy required to produce a unit of polymer. This energy requirement is largely determined by the compression energy required by the hyper compressor. Thus, there is a need to maximize polymer production by increasing ethylene conversion for a given amount of compression energy. The maximization of polymer production needs to be combined with maximization of the flexibility in product design, as expressed as the ratio of broad MWD to narrow MWD capability at a given melt-index. The extension of product design, while maximizing polymer output and/or reducing energy input, have been met herein.